A coordinated effort is planned to acquire greater understanding of the events involved in the development and specification of neural connections, the factors governing their stability, and the trophic, inductive influences exerted by one cell on another. These projects fall into two areas: (a) assessment of the trophic and inductive effects of nerves of different types on skeletal muscle. This includes the synapses formed by preganglionic autonomic nerves on frog skeletal muscle, the initial formation of synapses by the tadpole sciatic nerve on mature tail muscle (transplanted), and the influence of nerve and muscle inactivity in chick embryos. In addition, the role of nerve integrity, activity and axoplasmic transport will be analyzed in a mammalian in vivo neuromuscular preparation, and the effect of chronic directly-evoked contractile activity in transplanted frog muscle tested. (b) determination of the plasticity of respecification of retino-tectal connections in fish, coupled with behavioral analysis of the degree of function restored in cases of "compressed" optic nerve projection. A variety of tectal and retinal lesions, including tectal rotation, are planned as challenges to the system. A third area of investigation will be continued study of the ionic mechanisms of synaptic transmission in moth neuromuscular junctions, of interest because of the unusual ionic composition of moth haemolymph.